Arteriosclerosis is a genera term which refers to any of a group of diseases in which the lumen of an artery becomes narrowed or blocked. The most common and important form of arteriosclerosis, especially in Western societies, is the disease known as atherosclerosis. In atherosclerosis, there is an accumulation of lipids in the intimal, or inner, layer of the affected artery. The resulting intimal thickening restricts the flow of blood so as to hinder the functioning of, or permanently damage, the organ which the artery feeds. These accumulations of lipids tend to be localized and can occur in coronary, cerebral, or peripheral arteries. They will hereinafter be referred to synonymously as lesions, plaques, or atheromas.
The lipid accumulation is made up of free lipid and smooth muscle cells which have proliferated and taken up lipid. As the disease progresses, the lesion may begin to absorb calcium which causes it to harden and may also be composed of blood which has clotted in response to the presence of the atheroma. Although the process of plaque formation is not completely understood, it is known to be progressive, and atherosclerotic plaques may vary greatly in their physical characteristics.
Another cause of arterial narrowing, especially in patients with acute myocardial infarction (heart attack), is formation or embolization of a thrombus (clot) within a coronary artery.
Treatment of atherosclerosis and occlusive thrombi is aimed at alleviating the diminished blood flow. This can sometimes be done by medical means which cause the smooth muscles of the arterial walls to relax and thereby dilate the artery. Other treatment methods are directed toward physiological compensation for the reduced blood flow. In cases where the artery is severely occluded, however, there is no reasonable alternative but to try to re-establish a lumen of proper diameter. A number of surgical procedures have been developed toward this end. These include endarterectomy, in which the plaque or thrombus is surgically removed, and by-pass grafts, in which a segment of artery or vein from elsewhere in the body is removed and reattached in place of the occluded artery. These procedures are major surgical operations and present a number of disadvantages to a patient including financial cost, inconvenience, and the risk of complications associated with any major surgery. Therefore, in the past several years, methods of re-establishing the patency of an occluded artery have been developed which are relatively noninvasive and present less risk to a patient than conventional surgery. One such method is transluminal angioplasty.
Other parts of the body are subject to balloon dilation, such as the esophagus and uretha, which may have narrowing due to scarring or fibromuscular hyperplasia, which is abnormal inward growth of the normal living tissue of an artery or other vessel.